Justin Timberlake sings Happy Birthday to eight-year-old boy with autism in front of 25,000 fans

Justin Timberlake gave one eight-year-old boy a birthday present he will never forget.

The Mirrors singer led 25,000 fans in singing Happy Birthday to Julian Delan, who has autism, during a concert in California.

The boy's father Peter said on Facebook it was "a moment Julian will never forget".

His mother admitted in a blog that she was nervous about taking her son, fearing his "obsessions, his volume, his repetitiveness, his clumsiness" would annoy other fans.

Marika Delan said Julian was "knocking into the chairs and dancing and singing and yelling, 'It’s my birthday!! This is my present! This is my present! I LOVE YOU JT!!'".

But a group sitting in front of the family alerted the singer to Julian's special occasion, prompting the heart-warming moment.

"Before we knew what was happening, the group in front of us that had turned out to be so incredibly kind all night to our birthday boy, and these gorgeous girls who I was convinced would be totally annoyed by Julian, had captured Justin’s attention," his mother described.

"And then it happened. Justin Timberlake was singing Happy Birthday. They all were."